Photo-electric cell



May 1, 1928.

W. 5. SMITH ET AL PHOTO ELECTRIC CELL Filed Dec. 1927 p 11/7 )n'fullnew; W70 wag-M 45 Patented May 1, 1928.-

UNITED STATES PATENT OFFICE.

WILLOUGHBY STA'I'KAM SMITH, OF BENCHAMS, NEWTON POPPLEFORD, AND NORMAN WILLIAM MOLACHLAN, OF LONDON, ENGLAND.

PHOTO-ELECTRIC CELL.

Application filed December 5, 1927, Serial No This invention relates .to photo-electric cells and is applicable alike to photo-electric cells of the so-called gas filled or to the high vacuum type. The invention has for 6 ob ect the provision of a photo-electric cell whose elfective output can be readily controlled and in which the effects of interelectrode capacity are minimized or eliminated. In photo-electric cells of the kind in m which one or more control electrodes, for example of grid form are located within the cell between the cathode and the anode thereof there is normally a sluggishness in action due to the inherent capacity.

The inter-electrode capacity, more particularly that between the grid-like elec trode or electrodes and the anode, may be undesirable. For exam la, in a photo-electric cell having one gri -like electrode, servin as an in at electrode, capacity between this said grid-like electrode and the anode or output electrode may be very-undesirable for obvious reasons.

Incarrying out the present invention a glow-electric cell having a control electrode tween anode and cathode is rovided with one or more additional electro es adapted to act as an electrostatic screen or screens, and so formed as substantially not to impede an electron flow.

In one arrangement embodyin the present invention, a photo-electric ce provided with a control grid and an electrostatic screen is adapted to be operated b a moving as beam of light moving. relatively thereto. This is efi'ected by inserting in the path of the said bea'm a graded li ht filter or screen so that the intensity of ight falling upon the cell varies asthe beam and the screen 40 move relatively to one another.

If desired the aded light filter or screen 10 may be forme d as part of or attached to the window of the photo-electric cell. It will be seen that as the beam of light moves 4; across the window of the cell, the degree of 237,771, and in Great Britain August 8, 1926,

The invention is illustrated in the accompanying drawing which shows a hoto-elec: tric cell having a control gri and one screening grid between the input and output circuits of the cell.

Referring to the figure, 1 is an electrode having a coating of photo-electrically sensitive material, 2 an anode formed as in the known manner, of mesh work, 3 a control grid situated therebetween, and 4 a screenmg electrode formed as a mesh or Wire grid, or as a series of plates with slots, and interposed between the control grid 3 and the anode 2.

The electrode 4 is connected by way of its connection 4 to a point of relatively static potential (e. g. earth, either directly or through a battery as shown) sov as to act as an electrostatic screen. The mesh and general formation of the screening grid should be such as to permitsubstantially unimpeded electron flow to the anode.

The leads 1? 3 to the input electrodes should be well separated from the lead 2 to the output electrode, so as to avoid undesired capacity therebetween.

What we claim is A photo-electric cell comprising an envelope containing an electron emittin li ht sensitive cathode, an anode, a contro e ectrode situated between said anode and cathode an electrostatic screening grid between said control grid and said anode, external connection means for all of said electrodes,

the connection means for the anode being brought outside theenvelope at a point remote from that at which the connection for the cathode is brought out, and a graded light filter attached to said envelope.

In testimony that we claim the foregoing as our invention, we have signed our names this twenty second day of November, 1927.

wliioucim sum/m suml. norms wluml museum.

varied. 

